In hydraulic mounts such as those being used to an expanding degree to support an internal combustion engine in a motor vehicle, an orifice normally connects an expansible chamber with another chamber that is substantially less expansible and is defined by an elastomeric body connecting the mount's two mounting brackets. In such mounts, the orifice is normally of a prescribed fixed size and where variable damping is desired (e.g. high damping at low frequency and large amplitudes and low damping at high frequency and small amplitudes), it has become common practice to add a so-called "decoupler" that effects a volume displacement in the chambers such that no fluid is displaced through the orifice in relation to prescribed frequency and amplitude levels.